1. Field of the Invention
The present invention relates, in part, to the papermaking arts, and specifically to the fabrics, commonly referred to as paper machine clothing, on which paper is manufactured on paper machines. The present invention also relates to the manufacture of nonwoven articles and products by processes such as hydroentanglement, and specifically to the so-called industrial fabrics on which such articles are manufactured. More specifically still, the present invention concerns the bonding of structural elements, such as individual yarns or separate layers, of such fabrics to one another by methods in which polymeric resin materials are used as bonding agents and are deposited in a highly controlled and precise manner.
2. Description of the Prior Art
During the papermaking process, a cellulosic fibrous web is formed by depositing a fibrous slurry, that is, an aqueous dispersion of cellulose fibers, onto a moving forming fabric in the forming section of a paper machine. A large amount of water is drained from the slurry through the forming fabric, leaving the cellulosic fibrous web on the surface of the forming fabric.
The newly formed cellulosic fibrous web proceeds from the forming section to a press section, which includes a series of press nips. The cellulosic fibrous web passes through the press nips supported by a press fabric, or, as is often the case, between two such press fabrics. In the press nips, the cellulosic fibrous web is subjected to compressive forces which squeeze water therefrom, and which adhere the cellulosic fibers in the web to one another to turn the cellulosic fibrous web into a paper sheet. The water is accepted by the press fabric or fabrics and, ideally, does not return to the paper sheet.
The paper sheet finally proceeds to a dryer section, which includes at least one series of rotatable dryer drums or cylinders, which are internally heated by steam. The newly formed paper sheet is directed in a serpentine path sequentially around each in the series of drums by a dryer fabric, which holds the paper sheet closely against the surfaces of the drums. The heated drums reduce the water content of the paper sheet to a desirable level through evaporation.
It should be appreciated that the forming, press and dryer fabrics all take the form of endless loops on the paper machine and function in the manner of conveyors. It should further be appreciated that paper manufacture is a continuous process which proceeds at considerable speeds. That is to say, the fibrous slurry is continuously deposited onto the forming fabric in the forming section, while a newly manufactured paper sheet is continuously wound onto rolls after it exits from the dryer section.
Contemporary fabrics are produced in a wide variety of styles designed to meet the requirements of the paper machines on which they are installed for the paper grades being manufactured. Generally, they comprise a woven or other type base fabric. Additionally, as in the case of fabrics used in the press section, the press fabrics have one or more base fabrics into which has been needled a batt of fine, nonwoven fibrous material. The base fabrics may be woven from monofilament, plied monofilament, multifilament or plied multifilament yarns, and may be single-layered, multi-layered or laminated. The yarns are typically extruded from any one of the synthetic polymeric resins, such as polyamide and polyester resins, used for this purpose by those of ordinary skill in the paper machine clothing arts.
The woven base fabrics themselves take many different forms. For example, they may be woven endless, or flat woven and subsequently rendered into endless form with a woven seam. Alternatively, they may be produced by a process commonly known as modified endless weaving, wherein the widthwise edges of the base fabric are provided with seaming loops using the machine-direction (MD) yarns thereof. In this process, the MD yarns weave continuously back-and-forth between the widthwise edges of the fabric, at each edge turning back and forming a seaming loop. A base fabric produced in this fashion is placed into endless form during installation on a paper machine, and for this reason is referred to as an on-machine-seamable fabric. To place such a fabric into endless form, the two widthwise edges are brought together, the seaming loops at the two edges are interdigitated with one another, and a seaming pin or pintle is directed through the passage formed by the interdigitated seaming loops.
Further, the base fabrics may be laminated by placing at least one base fabric within the endless loop formed by another, and by typically needling a staple fiber batt through these base fabrics to join them to one another as in the case of press fabrics. One or more of these woven base fabrics may be of the on-machine-seamable type. This is now a well known laminated press fabric with a multiple base support structure. In any event, the fabrics are in the form of endless loops, or are seamable into such forms, having a specific length, measured longitudinally therearound, and a specific width, measured transversely thereacross. Also disclosed are “subassemblies” of various materials which are then spiraled or laid up in parallel strips to form substrates for press fabrics; the subassemblies are formed by techniques including lamination.
Turning now to industrial process belts, laminated structures are known in the textile industry. Lamination techniques are also used to form roll covers used in papermaking. One prior art belt is composed only of nonwoven fibrous material as the substrate. Also previously disclosed are laminated nonwovens for use as press fabrics with each layer has different properties such as hydrophobicity, and multiple extruded sheets as support structures for belts. Another prior patent teaches spirally winding strips of various types of materials to form a support structure for a belt. The prior art also teaches a substrate of expanded film, and narrow composite “tapes”. Additional prior art includes the following:
U.S. Pat. No. 3,042,568 shows a method and apparatus for the manufacture of laminated fabric belting. A heating chamber and pressure rollers are used to bond a plurality of lengths of plastic-coated fabric into a laminated unitary belt;
U.S. Pat. No. 3,673,023 shows a process for producing a reinforced laminate for use in belts where high tensile strength is required. The belts are made by laying helically wound, continuous reinforcing cords in what is essentially a screw thread or threads extending between the lateral margins of a base. The belt is finished by a top ply laid over the wound carcass, which is then cured with heat and pressure to form a consolidated belt structure;
U.S. Pat. No. 4,109,543 shows a composite laminate. The laminate comprises a hot-melt-type thermoplastic material and a textile woven fabric material formed of spun yarns constructed primarily of staple fibers. They are combined with each other using heat and pressure to form a belt; and
U.S. Pat. No. 5,240,531 shows an endless conveyor belt consisting of a core member and an elastic laminate layer. The layers are together passed through a pressing apparatus that bonds them together through the use of heat and pressure.
In the case of many applications, including woven fabrics, fabrics produced by spirally winding a strip of woven or knitted fabric (see U.S. Pat. No. 5,360,656 to Rexfelt), laminated fabrics all require some mechanism for either keeping the yarns in place or for joining the fabric together. Typically heretofor needling of staple fiber through a multilayer fabric was utilized to keep it together. Other methods as aforenoted were utilized such as bonding or welding.
The present invention provides another approach towards bonding and providing dimensional stability to fabrics.